Method and apparatus for preventing erroneous operation in non-contact push-button switch

ABSTRACT

To detect a faulty operation in a non-contact switch, a pulse signal is applied to the light emitting element of non-contact switch. The thus input pulse signal is compared with an output signal generated by a light receiving element of the non-contact switch. The faulty operation of the non-contact switch is discriminated in accordance with the thus compared input and output signals. Also to detect a faulty operation of the non-contact switch, a switch assembly includes a main push-button and an auxiliary push-button concentrically located over and within the main push-button. When the main push-button operates properly, the blocking members associated with the main push-button and the auxiliary push-button are displaced together. On the other hand, when the main push-button malfunctions, the light blocking member of the auxiliary push-button blocks the passage of light within the non-contact switch. Thus, an erroneous operation resulting from jamming of the main push-button is prevented.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a method and an apparatus for preventingerroneous operation in a non-contact push-button switch which is used asa pendant switch of hoist crane, for example.

2. Description of the Prior Art

Generally, as the pendant switch mentioned above, a contact typepush-button switch has been used. However, in operating the push-buttonswitch of this type, sparking takes place upon each operation resultingin an erosion of the contact and the service life of the switch isshortened. Also, in a low-voltage operation, an inferior contact takesplace and the crane operation thus lacks accuracy. Moreover, in the caseof a contact type multi-stage operation switch, the switch assembly mustbe made large.

In view of the above drawbacks of the contact type push-button switch,the present inventors previously suggested a non-contact typepush-button switch which utilizes light (Japanese Patent Application No.58-77860 and Japanese Patent Application No. 60-94294). This switchcomprises a luminous element, a light receiving element and apush-button having a light shading plate provided between both elementsand is designed so that light projection to the light receiving elementis selectively controlled according to the position of the push-button.

Since the above pendant switch is suspended from a hoist crane, it ismore readily subject to impact, vibration, etc.. That is, it mustoperate under severe conditions. Electronic parts of the push-buttonswitch will more readily break-down than electronic parts contained in acontrol box, for example, when the switch breaks, if an operation signalis not given in spite of the operation of the push-button, although thecrane is inoperable, the danger presented is minimal. However, if anoperation signal is given continuously in spite of restoring thepush-button to an OFF position, unintended movement of the crane willresult, thus creating a very dangerous situation.

SUMMARY OF THE INVENTION

The present invention has been made in view of the above. The firstobject of the present invention is to prevent erroneous operation due tothe malfunction of electronic parts of the non-contact switch.

The second object of the present invention is to prevent erroneousoperation which takes place when the push-button has a mechanicalmalfunction, namely, when the push-button does not return to theoriginal position due to the damage of a return spring or due to thewedging of foreign matter.

In order to attain the above first object, a method of preventingerroneous operation of a non-contact push-button switch of the presentinvention includes impressing pulse electric power to an input of thenon-contact switch, discriminating the acceptability of an output signalfrom the switch by comparing the output signal with the waveform of theimpressed pulse electric power at a discrimination circuit, andselecting and providing an operation signal to a driving circuit of aninverter, an electromagnetic contractor or the like.

According to the present invention, even if an ON operation signaloutput is given from the switch while the push-button is in an OFF statedue to a malfunction of electronic parts constituting the non-contactpush-button switch, an ON operation signal is not output from thediscrimination circuit and, accordingly, the OFF state is maintained andunintended working of the apparatus or other related trouble does nottake place.

In order to attain the above second object, the non-contact typepush-button switch according to the present invention includes apush-button assembly having a main push-button and an auxiliary buttoninserted into the main push-button, with a spring for returning theauxiliary button interposed therebetween. Light transmits by making alight transmitting window of a light shading plate and a lighttransmitting window of an auxiliary light shading plate coincide witheach other while the push-button is working normally. When the auxiliarybutton separates from the main push-button due to spring pressure, thelight transmitting window of the light shading plate is blocked by theauxiliary light shading plate.

According to the present invention, when the pressed down mainpush-button does not return to its original position due to damage ofthe return spring or due to some other reason, only the auxiliary buttonreturns and light projection is blocked by the auxiliary shading plate.Thus, a switch-off state is obtained.

BRIEF DESCRIPTION OF THE DRAWINGS

Features of the present invention will be understood more clearly fromthe following description made with reference to the accompanyingdrawings.

FIG. 1-FIG. 11 relate to embodiments of the present invention for theprevention of an erroneous operation due to the malfunction ofelectronic parts.

FIG. 12-FIG. 19 relate to embodiments of the present invention for theprevention of an erroneous operation due to the malfunction ofmechanical parts.

FIG. 1 is a block diagram of the basic electrical configuration of thepresent invention;

FIG. 2 is a waveform diagram of the configuration shown in FIG. 1;

FIG. 3(A) to (F) constitute an explanatory drawing showing relationsbetween switch input and switch output signals in the configurationshown in FIG. 1;

FIG. 4 is a circuit diagram detailing a discrimination circuit and asynchronous signal conversion circuit of the invention;

FIG. 5(A) to (E) constitute an explanatory drawing showing a modifiedpulse signal and output signals of the invention;

FIG. 6 is a circuit diagram of the first embodiment of the presentinvention;

FIG. 7 is a perspective view of a non-contact push-button switch used inthe embodiment of FIG. 6;

FIG. 8 is a circuit diagram of the second embodiment of the presentinvention;

FIG. 9 is a perspective view of the non-contact push-button switch usedin the embodiment of FIG. 8;

FIG. 10 is a circuit diagram of the third embodiment of the presentinvention;

FIG. 11 is a perspective view of the non-contact push-button switch usedin the embodiment of FIG. 10;

FIG. 12 is a cross section view of a non-contact push-button switch ofthe present invention;

FIG. 13 is a detailed view of a push-button switch assembly;

FIG. 14(A) is a front vertical section view in a normal OFF state, andFIG. 14(B) is a front vertical section view in which the spring 140 isin a damaged state;

FIG. 15(A) is a side vertical section view in a normal OFF state, andFIG. 15(B) is a side vertical section view in which the spring 140 is ina damaged state;

FIG. 16 is a detailed view of the push-button switch assembly during anON operation state;

FIG. 17 is a detailed view of the push-button switch assembly during amalfunction state;

FIG. 18(A) is a perspective view illustrating the auxiliary button 110Bfitted in the main button 110A in the normal OFF state, and FIG. 18(B)is an explanatory drawing illustrating the auxiliary button 110Barranged above the main button 110A and the state of both buttonsimmediately prior to fitting to each other; and,

FIG. 19 is a bottom view of a block proper switch housing in which aback plate and a base plate are removed.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 to FIG. 11 show embodiments of the present invention forpreventing erroneous operation due to a malfunction of the electricparts of the non-contact switch.

FIGS. 3(A)-(F) illustrate voltage waveforms for explaining the principleof detecting an erroneous operation according to the present invention.Each of FIGS. 3(A)-(F) denote the relation between an input electricpower applied to the switch and the output signal generated from theswitch, the switch including a luminous body and a light receiving bodyfor effecting a non-contact switching operation. FIGS. 3(A), (B) and (C)show the case where the input electric power source is direct constantcurrent; FIGS. 3(D), (E) and (F) show the case of input pulse electricpower.

FIG. 3(A) shows the case where the push-button switch works normally.That is, when an impressed electric power "a" is at a high level(hereinafter referred to as an H level), the output signal "B" when theswitch is ON is at a low level (hereinafter referred to as an L level),and when the switch is OFF, output signal "c" is an H level. GND denotesthe L level position.

FIG. 3(B) show the case where the luminous element of the switch doesnot properly emit light or where the light receiving element thereofdoes not work properly. In this case, irrespective of whether the switchis ON or OFF, output signals "d", "e" are at an H level.

FIG. 3(C) shows the case where the light receiving element is inoperative state (i.e. a light receive state), even though thepush-button is in an OFF state. In this case, the output signals "f" and"g" are at an L level, irrespective of whether the switch is actuallyintended to be ON or OFF. That is, the output of the switch alwaysappears ON.

FIG. 3(D) shows the case where a pulse electric power source is appliedto the switch and the switch works normally. In this case, the outputsignal "j" when the switch is ON is a pulse signal of reverse phaserelative to the impressed pulse electric power "h", and the outputsignal "k" when the switch is OFF is at an H level.

FIG. 3(E) shows the case where the luminous element does not properlyemit light or the light receiving element does not work properly,similar to FIG. 1(B). In this case, output signals "1" and "m" are at anH level, irrespective of whether the switch is ON or OFF.

FIG. 3(F) shows the case where the light receiving element is anoperating state (i.e. a light receiving state), even though thepush-button switch is in an OFF state. In this case, the output signals"n" and "p" of the switch are at an L level, irrespective of whether theswitch is ON or OFF.

The present invention applies pulse electric power to the push-buttonswitch and aims at preventing erroneous operation resulting frommalfunctioning electronic parts by discriminating output signals of thepush-button switch in comparison with the impressed pulse electricpower.

FIG. 1 is a block diagram of an apparatus for preventing erroneousoperation according to the present invention in which pulsed electricpower is applied to the push-button switch. A non-contact push-buttonswitch 1 includes a luminous element LED and a light receiving elementPT (photo-transistor, CD cell, photo-diode or the like) which are spacedfrom each other with a push-button PB therebetween. The push-button PBnormally (in the OFF position) blocks light emitted by the luminouselement LED from becoming incident on the light receiving element PT,and only when the push-button is pressed (ON), is light incident on thelight receiving element PT.

Control circuiting 2, which forms an erroneous operation preventiveapparatus for the non-contact push-button switch 1, includes a pulseelectric power source 3 and a discriminating circuit 4.

The pulse electric power source 3 impresses pulsed electric power on theluminous element LED, which radiates corresponding pulsed light.Referring to FIG. 2, by pushing the push-button PB (ON), light isprojected onto the light receiving element PT during the pressing time"t" and the output signal "j" of the push-button switch is issued as apulse signal of a reversed phase.

The output signal "j" is applied to the discrimination circuit 4. Thepulse voltage "h" is also applied to the discrimination circuit 4 fromthe electric power source 3, and the thus applied signals "j" arecompared on the basis of the pulse voltage "h".

That is, the output signals (ON, OFF output signals) of the push-buttonswitch as shown in FIGS. 3(D), (E) and (F) are compared with the inputpulse electric power. In the cases of FIGS. 3(D) and (E), the output ofthe push-button switch is at an H level when the electric power sourceis at an L level (the luminous element does not emit light),irrespective of whether the push-button is ON or OFF.

In consideration of the delay in the response of the light receivingelement PT, referring to FIG. 2, if the point j₁ of the output signal"j" of the push-button switch (which corresponds to the point h₁ wherethe electric power source pulse "h" rises to the H level) is at an Hlevel, the switch is judged to be normally operative, and if the outputsignal "j" at point j₁ of the push-button switch is at an L level asshown in FIG. 3(F), the switch is judged to be malfunctioning.

In order to carry out the above discrimination, the discriminationcircuit 4 uses a shift register (C-MOS4015B), for example, as shown inFIG. 4.

An input terminal 1A of the discrimination circuit (hereinafter referredto as the shift register) is connected to an output terminal of thelight receiving element PT. The input pulse for the push-button switch 1is also input to a clock input terminal TA, whereby the shift register 4transmits, via the output terminal Q1, the input to the input terminal1A in response to the rise of the electric power source pulse.Therefore, the output terminal Q1 signal is at an H level in the casesdepicted in FIGS. 3(D) and (E), and is at an L level in the casedepicted in FIG. 3(F). Thus, the desired discrimination is madepossible.

Thus, when the push-button switch is ON, the output of the circuit is apulse signal. It is not preferable to impress such a pulse signal to asucceeding logic operation circuit or to a driving circuit 5 (shown inFIG. 1), such as an output relay. Therefore, it is necessary to convertthe output pulse signal to a signal which changes its logic state insynchronism with the ON - OFF operation of the push-button PB as shownby signal "q" in FIG. 2.

As is obvious from FIG. 3(D) and FIG. 4, the light receiving element PTis in a light receiving state when the push-button PB is ON and theelectric power source pulse is at an H level. In consideration of thedelay of the light receiving element in response to the incident light,referring again to FIG. 2, if the point j₂ of the output signal of thepush-button switch is at an H level in relation to the point h₂ at whichthe electric power source pulse to the push-button switch moves from anH level (the luminous element emits light) to an L level, thepush-button switch can be judged as OFF, and if it is at an L level, thepush-button switch can be judged as ON.

Therefore, a synchronizing signal conversion circuit 6 for outputting asignal "q" which is synchronized with the ON-OFF operation of thepush-button switch can be composed as shown in FIG. 4, using a shiftregister (C-MOS4015B).

An output signal of the push-button switch 1 is input to an inputterminal 1B of the synchronizing signal conversion circuit 6(hereinafter referred to as a shift register), and a pulse which isinverted relative to the electric power source pulse applied to thepush-button switch 1 is inputted to the clock terminal TB, whereby theshift register 6 transmits, via the output terminal Q2, data input tothe input terminal 1B at the point where the electric power source pulsemoves from an H level to an L level. As a result, the output of theshift register 6 becomes an L level when the push-button PB is ON, andbecomes an H level when the push-button PB is OFF, and thus the desiredoutput signal "q" as shown in FIG. 2 can be obtained.

As shown in FIG. 5, if an electric power source pulse of the push-buttonswitch is generated as a pulse "ha" having long H level period and veryshort L level period, the output of the push-button switch 1 will take aform such as the waveform "ja". If this signal "ja" is amplified andthen applied directly on the coil of the relay, a contact state can bemaintained so long as the output "ja" of the push-button switch 1 isused. Thus, the synchronizing signal conversion circuit 6 forsynchronizing with the ON-OFF operation of the push-button can beomitted.

If the above waveform is passed through a CR integration circuit,fluctuation can be minimized as shown by signal "jb", and if it isfurther passed through a Schmidt circuit, the fluctuation of thewaveform almost vanishes and a signal "jc" in synchronism with theON-OFF operation of the push-button can be obtained.

FIG. 6 to FIG. 11 show examples of circuits to which the presentinvention can be applied. An operation circuit 10 of the firstembodiment shown in FIG. 6 is provided with two sets of switch units 12,13, each of which operates a rely 14 and a relay 15, respectively. Theswitch unit 12 includes a luminous element LED1, a light receivingelement PT1 and a push-button PB1 which is interposed between bothelements. The switch unit 13 includes a luminous element LED2, a lightreceiving element PT2 and a push-button PB2 which is interposed betweenboth elements.

The luminous elements LED1, LED2 and the light receiving elements PT1,PT2 are arranged as shown in FIG. 7. The push-button PB1 is providedwith a light shading plate 16. While the push-button PB1 is not pressed(OFF position), the light shading plate 16 blocks light projected fromthe luminous element LED1 from becoming incident on the light receivingelement PT1, but allows light projected from the luminous element LED2to become incident on the light receiving element PT2. In contrast,while the push-button PB1 is pressed (ON position), light is projectedto the light receiving element PT1, but is blocked from the lightreceiving element PT2. The other push-button PB2 is similarly providedwith a light shading plate 17, which selectively blocks projected lightas shown in FIG. 7. Thus, when both push-buttons PB1, PB2 are notpressed (OFF position), light is not incident on either of the lightreceiving elements. Similarly, when both push-buttons are pressed (bymistake, for example) light is not incident on either of the lightreceiving elements and erroneous operation is prevented.

Referring again to FIG. 6, reference numeral 18 (FIG. 6) denotes a pulsepower supply circuit using an IC for timer (555) purposes.

The input pulse in this embodiment is a waveform "ha" shown in FIG. 5(i.e. a waveform having a long H level period and very short L levelperiod).

The output of each of the light receiving elements PT1, PT2 is appliedto discrimination circuits 19, 20 (each formed of a shift register asmentioned above) in response to selective pressing of the push-buttonsPB1, PB2, and the acceptability of each output signal is judged by eachshift register. The output and a push-button signal are input and,together with an ON signal from the light receiving element PT1, operatea relay 14 through an amplification circuit 21. Similarly, when an ONsignal from the light receiving element PT2 is given, a relay 15 isoperated through an amplification circuit 22.

NOR gate 23 is provided for preventing erroneous operation of thepush-button 11. The NOR of the two push-button output signals are inputto reset terminals RA, RB of the shift registers 19, 20, and when ONsignals are given from the light receiving elements PT1, PT2 at the sametime, output signals from the shift registers 19, 20 are regarded as thesame, as inferior signals, and are interlocked.

FIG. 8 and FIG. 9 show a second embodiment.

A non-contact push-button switch 31 of an operation circuit 30 includesa luminous element LED1, two light receiving elements PT1, PT2, aluminous element LED2, two light receiving elements PT3, PT4 and twopush-buttons PB3, PB4. By two-step (two-stage) shifting of thepush-buttons PB3, PB4, relays 32, 33, 34 are selectively operated.

As shown in FIG. 9, push-buttons PB3, PB4 are provided with lightshading plates 35, 36. The light shading plate 35 blocks light projectedto the light receiving elements PT1, PT2 when the push-button PB3 is notpressed (OFF position), allows light to project only to the lightreceiving element PT1 when the push-button PB3 is pressed a first step,and allows light to project to both light receiving elements PT1, PT2when the push-button PB3 is pressed a second step. Light can beprojected to the light receiving elements PT3, PT4 only when thepush-button PB3 is in an OFF position, such light being blocked when thepush-button PB3 is pressed the first and second steps.

Similarly, as is readily apparent from FIG. 9, the light shading plate36 fitted to the other push-button PB4 allows selective light projectionto the light receiving elements PT3, PT4.

Referring again to FIG. 8, reference numeral 37 denotes a pulse electricpower source for generating a waveform pulse having a long H levelperiod and very short L level period.

The output of each light receiving element PT1, PT2, PT3, PT4 is appliedto a discrimination circuit formed of a shift register as mentionedabove, and the discriminate output signals and signals from each lightreceiving element PT1, PT2, PT3, PT4 of the push-button switch 31 areapplied to amplification circuits 40, 41, 42 for operating relays 32,34, 34 as shown.

Signals from light receiving elements PT1, PT3 are applied to NOR gate44 and the output thereof is input to a reset terminal RA of adiscrimination circuit 38 (shift register), whereby when ON signals aregiven from the light receiving elements PT1, PT3 at the same time, theshift register 38 is reset and both signals are interlocked.

This embodiment illustrates the case where output signals of the lightreceiving elements PT2, PT4 are applied to a synchronizing signalconversion circuit 43 for converting to signals which synchronize withthe ON-OFF operation of the push-buttons PB3, PB4.

FIG. 10 and FIG. 11 how a third embodiment. A non-contact push-buttonswitch 51 of a circuit 50 includes a luminous element LED1, two lightreceiving elements PT1, PT2, a luminous element LED2, two lightreceiving elements PT3, PT4 and a pair of push-buttons PB5, PB6. Bythree-step shifting of the push-button, four relays 52, 53, 54, 55 areselectively operated.

As shown in FIG. 11, the push-buttons PB5, PB6 are respectively providedwith light shading plates 56, 57. The light shading plate 56 interceptslight projected to light receiving elements PT1, PT2 when thepush-button PB5 is not pressed (OFF position), allows light to projectonly to the light receiving element PT2 when the push-button PB5 ispressed a first step, allows light to project to both light receivingelements PT1, PT2 when the push-button PB5 is pressed a second step, andallows light to project only to the light receiving element PT1 when thepush-button PB5 is pressed a third step.

Light can be projected to the light receiving elements PT3, PT4 onlywhile the push-button PB5 is in an OFF position and becomes blocked whenpressed the first, second and third steps.

Similarly, as is readily apparent from FIG. 11, the light shading plate57 fitted to the push-button PB6 allows selective light projection tothe light receiving elements PT3, PT4.

Referring again to FIG. 10, reference numeral 58 denotes a pulseelectric power source circuit using an IC for timer (555) purposes. Theoutput waveform pulse has a long H level period and a very short L levelperiod.

The output of each light receiving element PT1, PT2, PT3, PT4 is inputto a discrimination circuit 60 through NAND gates 70, 71. The outputsignals of the light receiving elements PT2, PT4 are input to asynchronizing signal conversion circuit 63 through NAND gate 72 togenerate output signals which synchronize with the ON-OFF operation ofthe push-button. Each of such output signals and signals of PT2, PT3,PT4 which passed through the NAND gates are input to selective circuits61, 62.

By using a binary decoder (C-MOS, 4555B), for example, the selectivecircuits 61, 62 select the input O of the E terminal (the output of thediscrimination circuit 60 is at an H level and the electronic partsnormally operative) into output terminal Q1, Q2, Q3 due to an inputvariation (0 or 1) of terminals A, B and outputs it. When the input ofthe E terminal is 1 (the output of the discrimination circuit 60 is atan L level and electronic parts are inoperative), selective circuits 61,62 are reset and the output is made OFF.

When the push-button PB5 is ON, Q1 of the decoder 61 becomes 1 and isamplified by an amplification circuit 64 to drive the relay 52. When thepush-button PB6 is ON, Q2 of the decoder 61 becomes 1 and is amplifiedby an amplification circuit 65 to drive the relay 53.

The step to which the push-buttons PB5 and PB6 were pressed is judged bythe decoder 62. More particularly, at the time of a two step operation,Q3 of the selective circuit 62 becomes 1 and is amplified by anamplification circuit 66 to drive the relay 54, and at the time of athree step operation, Q1 of the selective circuit 62 becomes 1 and isamplified by an amplification circuit 67 to drive the relay 55. Thus,the step to which the push-buttons PB5 and PB6 were operated is realizedby the operation of the relays 52, 53, 54, 55.

According to the present invention, pulse electric power is used as aninput for operating a non-contact push-button switch, the output signalfrom the switch is compared with a waveform of the pulse input signal,and only when the switch output signal is judged to have a normal pulsewaveform, is an operation signal given. Therefore, in the event that an"ON" output is given from the switch even though the push-button is inan OFF state due to a malfunction of electronic parts constituting thenon-contact push-button switch or due to some other reason, an "ON"operation signal is not output from the discrimination circuit andunintended working of the apparatus does not take place.

Furthermore, the non-contact push-button switch according to the presentinvention has a construction including a luminous element, a lightreceiving and a push-button having a light shading plate interposedbetween the luminous element and the light receiving element, and pulseelectric power is input to the luminous element. Under thisconstruction, even if a signal line, a power source line of the luminouselement and an earth line make cross-contact in a cable between thepush-button switch and the control box, such can be judged by thediscrimination circuit and an operation signal is not given. Thus,safety is ensured.

FIG. 12 to FIG. 19 relate to the prevention of an erroneous operation ofthe push-button switch due to mechanical failures. Like parts aredesignated by like reference numerals in FIGS. 12-19.

As shown in FIGS. 12-19, reference numeral 100 designates a housing ofthe push-button switch made of material which is light weight, durableand insulating, such as synthetic resin. The housing 100 has at the backthereof two push-button inserting grooves 101 through which two opposingpush-buttons 110 are inserted. A light shading plate inserting groove102 opens at its both ends into the respective push-button insertinggrooves 101. Each push-button 110 is provided with a light shading plate111. The size of the light shading plate inserting groove 102 is suchthat when each push-button 110 is inserted into a respective push-buttoninserting groove 101, each light shading plate 111 is inserted into thelight shading plate inserting groove 102, overlapping each other.Provided at the central part of the housing 100 are element insertinggrooves 103, 104 (FIG. 19), having inserted thereto a light receivingelement PT (photo-transistor, CDS cell, photo-diode or the like) and aluminous element LED which are opposed to each other with the lightshading inserting groove 102 interposed therebetween. In the embodimenttwo element inserting grooves 103, 104 are arranged in parallel so thattwo sets of light receiving elements and luminous elements are used, butit is possible to use only one set of elements. In the case where asingle pair of luminous element and light receiving element is used, thesingle stage (or step) ON-OFF operation is carried out. In the case oftwo-stage or three-stage operation, two pairs light receiving elementsare used. The element inserting grooves 103, 104 open only at the bottomsurface of the housing 100 and one element is inserted independentlyinto each groove. A light transmitting hole (not shown) is made in theinner wall of this groove so that the light of the luminous elementreaches the side of the light receiving element.

The outer shape and the size of the push-button 110 are determined sothat the push-button 110 does not vibrate and slides smoothly in thepush-button inserting groove 101. The push-button 110 includes a mainpush-button 110A and an auxiliary button 110B slidably disposed on theupper outer periphery of the main push-button 110A. A hole is made in alateral direction at the lower part of the main push-button 110A and inthis hole, a spring S and a ball B for action are disposed. A steppedsurface 100A is formed at the inside surface of the push-buttoninserting groove 101 of the housing 100. This stepped surface 100A,together with the ball B which is pressed by the Spring S, makes itpossible to carry out the pressing down operation of the push-button instages (two-stage or three-stage).

An explanation is given below regarding the main push-button 110A.

A pushing piece 112 is provided at the top surface of the mainpush-button 110A and a spring stop projection 113 is provided at theopposite side of the pushing piece 112. A light shading plate 111provided at the side of the pushing piece 112 has at its upper endportion a light transmitting window 114 to permit the light of theluminous element on the push-button side to reach the opposite lightreceiving element when the push-button is pressed down. A push-buttonlight shading piece 115, which intercepts the light between bothelements of the other push-button when the push-button is pressed down,is provided at the outer end portion of the light shading plate 111. Thelight shading plates 111 of the two push-buttons are located so that thelight transmitting window 114 of one of the push-buttons corresponds tothe pushed-down light shading piece 115 of the other push-button.

An auxiliary button 110B is mounted on a hollow member 116 disposed atthe top surface of the main push-button proper 110A. A pushing piece118, which is located on the pushing piece 112, is provided protrudinglyat the upper part of a main part 117 of the auxiliary button 110B, andan auxiliary light shading plate 119 is provided at one side end of themain part 117 (FIG. 18(B)).

When the pushing piece 112 of the main push-button 110A is fitted in thepushing piece cavity 118h of the auxiliary button 110B, a spring 110S isinterposed between the top surface of the pushing piece 112 and theinner ceiling surface of the cavity 118h. By the action of the spring110S, the main push-button 110A and the auxiliary button 110B are forcedto separate from each other. The auxiliary light shading plate 119 ofthe auxiliary button 110B, when the main push-button 110A worksnormally, operates together with the light transmitting plate 111, andwhen the main push-button 110A is unreturnable due to damage of a returnspring 140 (to be described later) or due to some other reason, theauxiliary button 110B returns in such a manner that it is pushed up bythe spring 110S and blocks the light transmitting plate 111.

A small hole 118a is made at the top surface of the pushing piece 118 ofthe auxiliary button 110B and by inserting a fine rod R in this hole118a, the pushing piece 112 of the main push-button 110A can be pusheddown and it is thus possible to confirm whether or not the push-button110 is out of order.

A base plate 120 is of a size that can be fitted in a guide 107 providedaround the bottom of the housing 100 and is provided with printedwiring. The luminous element LED and the light receiving element PT arearranged on the base plate 120. The one or more pairs of the luminouselement LED and the light receiving element PT are opposed to eachother. These elements are inserted in the element inserting grooves 103,104 of the housing 100.

A bottom lid 130 is provided at the bottom of the housing 100 in such amanner that presses and fixes the base plate 120. The bottom lid 130 isintended to prevent the penetration of dust into the housing and is madeof an insulating material. The bottom lid 130 is provided with supportparts 131, 132 which support the spring 140.

In assembling the parts of the above construction, as shown in FIG. 12,two opposite push-buttons 110 are inserted in the push-button insertinggrooves 101 in such a manner that light shading plates 111 overlap eachother and the pushing piece 112 projects from the top surface of thehousing 100. In this case, the pushing piece 112 of the main push-button110A is inserted in the pushing piece cavity 118h of the auxiliarybutton 110B through the medium of the spring 110S.

The base plate 120 with luminous elements and light receiving elements(print wiring) is then provided for the back of the housing 100. At thistime, the light receiving element PT and the luminous element LED areinserted accurately in the element inserting groove 103 and the elementinserting groove 104, respectively.

Next, the bottom lid 130 is fitted in and fixed to the guide 107 whilethe spring 140 is inserted in the spring support part 131, 132. Sincethe elastic force of the spring 104 is stronger than that of the spring110S, the spring 110S is held in a compressed state. The housing 100carries a fitting piece 109 having a fitting screw hole 109a tofacilitate fitting to a switch case or the like.

When a push-button is pressed, it is pushed down against the force of aspring and the light from a luminous element on the side of thatpush-down reaches a light receiving element through a light transmittingwindow of a light shading plate which was pushed down, whereby the lightis converted into an electric signal for the desired operation. At thistime, the light from a luminous element on the other side is blocked bya push-down light shading piece of that push-button. Therefore, if bothpush-buttons are pressed by mistake, both are placed in an OFF state andthe switch does not work.

When the switch works normally as mentioned above, since the elasticforce of the spring 140 is stronger than that of the spring 110S, thespring 110S is in a compressed state and therefore the main push-button110A and the auxiliary button 110B are united. Under this condition,both the light shading plate 111 and the auxiliary light shading plate119 are pushed down with their light transmitting windows coincidingwith each other, whereby light is transmitted in an optical path of thetransmitting windows of the light shading plates 111, 119 and the switchis placed in an ON state.

There are cases where the push-button is placed in pressed down statedue to breaking of the return spring 140 or due to jamming (or wedging)of foreign matter, and the push-button thus does not restore to anoriginal state when the pressing down force is released. At such time,even if the switch is released, the switch ON state is maintained and itis impossible to place the switch in an OFF state. According to thepresent invention, even when the main push-button 110A is unrestorableto the original state due to damage of the spring 140 or due to someother reason, if the pressing down force is released, only the auxiliarybutton 110B is pushed up by action of the spring 110S, whereby theauxiliary light shading plate 119 of the auxiliary button 110B coincideswith the light transmitting window 114 of the light shading plate 111 ofthe main push-button 110A and closes the light transmitting window 114.Thus, the light is blocked by the auxiliary button 110B even though themain push-button proper 110A is not restored an OFF position when thepressing down operation is released. The switch is turned OFFirrespective of whether or not the main push-button 110A is restored toits original position and safety can be maintained.

What is claimed is:
 1. A non-contact switch comprising:a housing; alight emitting element and a light receiving element located within saidhousing, a push-button assembly located within and protruding from saidhousing, said push-button assembly comprising: a main push-button havinga first shading plate fixed thereto, said main push-button having a topportion located outside of said housing, a bottom surface located withinsaid housing and a hollow interior, a first spring applying an upwardforce against said bottom surface of said main push button; an auxiliarypush button concentrically located along an outer periphery of said mainpush button and having a second shading plate fixed thereto; and asecond spring located within said hollow interior of said main pushbutton and applying an upward force against said auxiliary push button;wherein, upon a downward force applied to said main push button and saidauxiliary push button, said first and second shading plates are togetherdisplaced to permit a passage of light from said light emitting elementto said light receiving element; wherein, when said downward force isremoved and said main push-button operates properly, said first andsecond shading plates are together displaced to an original position toblock said passage of light from said light emitting element to saidlight receiving element; and wherein, when said downward force isremoved and said main push-button operates improperly, only saidsimilarly push-button returns to the original position to clock saidpassage of light.